It is well known to assemble innerspring assemblies for mattresses and the like from pocketed coil springs. Typically, chains of pocketed springs are manufactured by feeding the springs direct from a spring coiling machine into the space between two plies of a weldable fabric, the two plies then being sealed together to form a pocket which encapsulates the spring. The fabric is then indexed forward, the next spring encapsulated, and so on. In this way, lengthy chains of pocketed springs are built up. Such chains of pocketed springs are referred to herein as “strings” of springs.
An innerspring assembly of appropriate dimensions for a mattress can then be built up by placing appropriate lengths of pocketed spring chain side by side and adhering them together.
Automated methods for forming innerspring assemblies in this way, and apparatus for carrying out such methods, are known. European Patent No 0154076, for example, discloses a method in which an adhesive applicator is passed over a string of pocketed springs, the applicator being actuated briefly as it passes over each spring so as to apply a line of adhesive to the spring, parallel to the lines defining the transverse sides of the pockets, and then contacting the string of springs against another similar string of springs.
European Patent No 0421495 discloses another method in which a string of pocketed springs is passed longitudinally past a fixed adhesive applicator such that adhesive is applied to one side of the string, which is then pressed into contact with a corresponding side of a second string of springs.
In both of the above methods the amount of adhesive applied to the various springs in each string is substantially the same. This can be a disadvantage in that it results in the innerspring assembly having a uniform degree of firmness along its whole length. Sometimes it is desirable for the firmness of the innerspring assembly to vary along its length. For instance, it is known to manufacture a mattress with three zones of firmness, the central region, which carries the greatest part of the weight of a person lying on the mattress, being relatively stiff, whilst the head and foot parts of the mattress are less stiff for greater comfort. A more sophisticated arrangement is a five zone mattress in which the central part is again the stiffest, but the extreme ends are also somewhat stiffer than the intermediate regions. Such arrangements cannot easily be produced using known innerspring assembly apparatus. Another disadvantage of the known systems is that the need to move the string of springs past a fixed adhesive applicator, or to move an applicator over a string of springs, may slow down the manufacturing process.
There have now been devised a method and apparatus for the manufacture of innerspring assemblies, which overcome or substantially mitigate the above-mentioned or other disadvantages of the prior art.